1. Field of the Invention
The present invention relates generally to dental implants, and more particularly to a dental implant assembly of the type having an implant portion for osseointegration in alveolar bone and an abutment portion securable to the implant portion for supporting a dental prosthesis.
2. Background Information
One known arrangement for a dental implant involves an implant portion, or artificial root, that is received in a hole prepared in alveolar bone, and an abutment, or prosthesis support, that is securable to the implant portion and that extends beyond the gingival tissue to support a tooth prosthesis. The implant portion and the abutment are constructed as separate components that are secured together by means of a screw passed through the abutment and received within a threaded bore in the implant portion.
In a first surgical procedure, an incision is made in the gingival tissue to expose the alveolar bone. Following any dressing of the surface of the bone that may be necessary, a hole that is complementary in shape to the implant portion is drilled in the bone and the implant portion is inserted. A healing cap or screw is attached to the implant portion to occlude the threaded bore, and the gingival tissue is stitched closed over the implant portion to await osseointegration.
In a subsequent second operation, following osseointegration of the implant portion, the gingival tissue is again opened to expose the implant portion. The healing cap or screw is removed and replaced with a second healing cap having an outer surface corresponding in shape below the gumline to that of the abutment, but protruding slightly above the gingival tissue. The gingival tissue surrounding the second healing cap is sutured thereabout to await healing in conformity to the outer surface of the second healing cap. After the gingival tissue has healed, the second healing cap is removed and replaced with a permanent abutment supporting a tooth prosthesis fashioned thereon.
In addition to providing a screw to secure the abutment to the implant portion, it is also known to configure the interface between the abutment and implant portion to resist rotation of the abutment relative to the implant portion. One such configuration involves a raised hexagon protruding from the abutment-engaging end of the implant portion that is received in a complementary hexagonal recess in the implant-engaging end of the abutment. Alternatively, it is known to provide the hexagonal recess in the implant and the raised hexagon on the abutment. Such arrangements not only provide resistance to rotation, but provide for indexing of the abutment in a plurality of angular orientations relative to the implant.
Another anti-rotation configuration is illustrated in U.S. Pat. No. 5,125,840 to Durr et al., issued Jun. 30, 1992, which shows a base body for implantation in bone that is provided with a threaded internal bore. In the upper end, a recess is formed that is of a larger diameter than the threaded bore to provide a stop shoulder at the junction of the recess and threaded bore. The stop shoulder is provided with four circumferentially spaced pockets. A ring member, or abutment, is provided with a centering collar having an external diameter that corresponds to the diameter of the recess of the base body. The centering collar has four circumferentially spaced tongues which are complementary to the interlocking pockets of the base body and coact therewith to prevent twisting between the ring member and the base body. A screw is received through the ring member and threadedly received in the threaded bore of the base body to secure the ring member to the base body.
One factor that is considered important by those persons who implant dental implants is the tactile feedback that is provided as the abutment is seated on the implant portion. During assembly of the abutment to the implant, it is important that tactile feedback be provided to positively indicate that the abutment is fully seated on the implant before the securing screw is tightened. Where anti-rotation features that permit indexing are provided, it is also useful to provide for piloting of the abutment on the implant to assist in aligning the abutment axially with the implant prior to seating the indexing features.
The complementary hexagon arrangement provides positive indication of seating in that the abutment moves suddenly in the axial direction through the full length of engagement of the hexagonal surfaces as the complementary surfaces become aligned. There is, however, no piloting of the abutment relative to the implant prior to complete alignment of the hexagons, and thus no assistance is provided to maintain the abutment and implant in axial alignment as the abutment is rotated to align the hexagons.
The arrangement shown in Durr provides for piloting of the abutment relative to the implant since the centering collar of the ring member is received in the recess of the base member prior to the tongues of the ring member engaging the pockets of the base body. However, due to the depth of the recess, the ring member travels more than half its ultimate length of engagement with the base; body before the tongues and pockets even begin to engage. Thus, it is possible that the initial axial displacement could be mistaken for complete seating of the ring member relative to the base member, without the tongues and pockets having engaged.